1. Field of the Invention
The present invention relates to a follow-up cruise control apparatus which prevents a collision with an obstacle ahead by detecting distances to front obstacles (including vehicles) present in a front area ahead of own vehicle including a straight-ahead course of own vehicle to correct a driving power or a braking power through a driver's pedaling action, or automatically controls the distance to the obstacle by controlling the driving power or the braking power of own vehicle.
2. Description of the Related Art
There have been conventionally proposed apparatuses which select a vehicle to be followed-up, from among obstacles ahead detected through radar, to assure own vehicle to safely cruise without the risk of collision with the obstacles.
Japanese Unexamined Patent Publication No. 5-342500 discloses such an apparatus. This apparatus is provided with a radar which scans a predetermined sector angle by emitting an electromagnetic wave in a traveling direction of own vehicle, and measures a distance to a reflective body based on a travel time which the electromagnetic wave takes to return back to the radar. The radar also detects reflectors arranged along one side of a lane, from among a plurality of reflective bodies. A lane estimating unit estimates the configuration of the lane based on the layout of a group of reflectors. A vehicle recognition unit recognizes the vehicles present ahead of own vehicle from among the reflective bodies. A lane determining unit determines whether the front vehicles recognized are present in the same lane as that of own vehicle. A vehicle-to-vehicle distance output unit outputs a vehicle-to-vehicle distance to the vehicle closest to own vehicle from among the vehicles present in the same lane.
The apparatus selects an obstacle A ahead of own vehicle as a vehicle of interest to be followed-up when own vehicle, and obstacles A and B run in two separate lanes under a condition (condition 1) as shown in FIG. 32A. Under the condition 1, the obstacle A is the one which the driver intends to follow, and the driver may be at ease with own vehicle which is controlled with the front obstacle A handled as a vehicle to be followed-up.
In FIG. 32B, own vehicle and an obstacle C run in the same lane with the obstacle C handled as a vehicle to be followed-up by own vehicle. Under a condition 2, an obstacle D now attempts to somewhat forcibly enter between own vehicle and the obstacle C. Own vehicle cannot change to the front obstacle D from the vehicle to be followed-up (the front obstacle C) under the condition 2 until the obstacle D has completed the change of lane. In this case, the drive may feel a chill, worrying about the risk of a collision.
Referring to FIG. 32C, own vehicle and the front obstacle E are now running in the same lane. The obstacle E is the vehicle to be followed-up by own vehicle. Under a condition 3, own vehicle now attempts to change to the lane in which an obstacle F is now running. Under the condition 3, own vehicle cannot switch the vehicle to be followed-up from the obstacle E to the obstacle F until own vehicle determines that the front obstacle F is running in the same lane of own vehicle's. As under the condition 2, the driver may also be ill at ease under the condition 3, as well.
Under the conditions 2 and 3, own vehicle must select, as a vehicle to be followed-up, in follow-up control, a vehicle having the highest degree of risk of collision with own vehicle, from among a plurality of front obstacles, rather than selecting a vehicle based on whether the vehicle runs in the same lane. The risk of collision needs to be determined referring to the following factors in the relative positional relationship between own vehicle and the front obstacles.
Relative distance of own vehicle in the travel direction thereof (hereinafter referred to as a traveling direction distance) PA1 Relative speed of own vehicle in the travel direction (hereinafter referred to as a traveling direction relative speed) PA1 Relative distance in a direction perpendicular to the travel direction of own vehicle (hereinafter referred to as a lateral distance) PA1 Relative speed in a direction perpendicular to the travel direction of own vehicle (hereinafter referred to as a lateral speed), and further, PA1 Acceleration and deceleration of the front obstacle PA1 Configuration of a road, and PA1 Relative position of own vehicle and the front obstacle with respect to a lane.
Japanese Unexamined Patent Publication No. 10-338055 discloses an apparatus which is free from the problems encountered under the conditions 2 and 3. This apparatus, provided with a vehicle-to-vehicle distance sensor for measuring a distance between own vehicle and each of a plurality of front obstacles, sets a target vehicle-to-vehicle distance to each of the plurality of the front obstacles, and calculates an acceleration and deceleration to each front obstacle from a difference between the vehicle-to-vehicle distance and the corresponding target vehicle-to-vehicle distance. By processing an image of the front obstacles picked up by a CCD (Charge-Coupled Device) camera, the apparatus detects the change of lane by own vehicle or by any of the front obstacles. The apparatus selects a minimum target acceleration and deceleration, and controls the engine output and braking power of own vehicle in accordance with the target acceleration and deceleration.
When the front obstacle D attempts to forcibly enter between own vehicle and the obstacle C under the condition 2, the apparatus selects, as a vehicle to be followed-up, either the obstacle C or the obstacle D, whichever exhibits smaller acceleration and deceleration. If the obstacle D applies the brake, own vehicle has a higher risk of collision with the obstacle D than with the obstacle C. The obstacle D exhibits smaller target acceleration and deceleration than the obstacle C, and the vehicle to be followed-up is immediately switched from the obstacle C to the obstacle D. This arrangement frees the driver from feeling a chill from the risk of collision.
When own vehicle changes to the next lane, in which the front obstacle F is running, under the condition 3, the apparatus selects, as the vehicle to be followed-up, the front obstacle E or the front obstacle F, whichever exhibits smaller target acceleration and deceleration. If the obstacle F applies the brake, own vehicle runs a higher risk of collision with the obstacle F than with the obstacle E. The front obstacle F exhibits smaller target acceleration and deceleration than the front obstacle E, and the vehicle to be followed-up is immediately shifted from the front target E to the front target F. In the same way as under the condition 2, the apparatus frees the driver from feeling a chill from the risk of collision.
As discussed above, the apparatus, disclosed in Japanese Unexamined Patent Publication No. 10-338055, employs detecting means for detecting the change of lane by a front obstacle and detecting means for detecting the change of lane by own vehicle. The two means play a vital role in the determination of the switching timing of the vehicle to be followed-up, therefore, in freeing the driver from feeling a chill from the risk of collision. The disclosure fails to describe in detail how the detecting means for detecting the change of lane by a front obstacle and detecting means for detecting the change of lane by own vehicle are embodied. Since the disclosed apparatus detects the change of lane by the obstacle and own vehicle using a CCD camera rather than a vehicle-to-vehicle sensor, the apparatus and the processing steps carried out by the apparatus become extremely complicated.